Behind a nearly incomprehensible title — at least for non-German-speakers — lies an attractive session of chamber improv by two versatile Swiss musicians who mix free music with a piano prepared according to the stricture of American composer John Cage.

Die Abwesenheit des Igels Beim Einbrechen der Nacht translates as the absence of the hedgehog as night falls, but except for some scurrying abrasive thumps on the pianos copper and steel strings during the first nine tracks, the animal reference seems awfully ambiguous.

Luckily you cant say the same thing about the playing of pianist Urban Mäder and bassist Christian Hartmann. As Mäder uses a combination of high intensity timbres and pedal pressure to amplify his thoughts, the bassist provides the pedal point extended with electronics to provide an ever-shifting showcase for the piano work.

Working both sides of the jazz/classical fence is second nature for these Lucerne-based musicians. Conservatory-trained, Mäder is a New music composer usually involved with installations or interdisciplinary projects. Hartmann is a baroque music specialist who also plays Free Jazz with fellow Swiss improvisers like pianist Guerino Mazzola and percussionist Heinz Geisser.

On the nine hedgehog pieces — most of which clock in around the two minute mark — Mäder and Hartmann seem most concerned with how many different sounds they can extract from their instruments. Short phrases mean that here the bassist is mostly limited to walking, scratching or occasionally buzzing his strings. On the other hand, strict adherence to Cages 1946 rules for prepared piano means that the keyboard and soundboard expel echoing low-frequency vibrating echoes, and also produce tones that variously resemble the ringing of a vibraharps metallic bars; the wooden timbre of a marimba; and the plink of miniature toy piano keys.Additionally, Mäder creates a percussive undercurrent with cascading tremolos, while maintaining a steady beat with strummed octaves.

More expansive, but usually taken at tempos that range from adagio to andante, the five additional creations, collectively titled Beim Einbrechen der Nacht — As Night Falls — at least give the bassist a chance to stretch out. Tugging forcefully on his strings hes able to create an underlying continuum plus some dramatic higher-pitched thrusts with the other hand. While the pianist usually concentrates on vibrating tremolos and metronomic dynamics — sounding a little stiff and so-called legit, in fact — he introduces free improv devices such as an arco drone, thumps on the instruments sides plus a section built out of manipulating the strings on the neck just below the tuning pegs. A solo track dedicated to him, involves using a forceful grip to prolong different tones. Other pieces depend as much on the silence and spaces between the piano notes and vibrating reverberations as anything else. Oddly enough on the very first night track with the bassist time-keeping in the most traditional manner, Mäders rolling arpeggios sound almost exactly like Lennie Tristanos 1950s and 1960s solo work.

Interesting in exposing the thought process of a composer turning improv wannabe, the CD can mostly be appreciated for the way Hartmann allows Mäder to express his version of freedom.